1. Field of the Invention
This invention relates to water-content hydraulic fluids and more particularly a concentrate for addition to water for the preparation of water-content hydraulic fluids. The invention further relates to a method of lubricating with water-content hydraulic fluids which may contain up to 95% or more water.
2. Description of the Prior Art
Heretofore, the technology of lubrication generally centered about the development of petroleum oils for lubricants or greases and the application of the lubricant so prepared to the point of wear or friction. Innumerable and complex lubricating compositions have been proposed comprising, generally, a hydrocarbon oil, a bodying or thickening ingredient and various additive agents designed to enhance the lubricant with respect to viscosity, foam stability, antiwear, and corrosion prevention properties. More recently, current interest has been directed to the preparation of aqueous lubricants, particularly water-content hydraulic fluids, due to the increasing cost of petroleum oils, the problem of flammability and the ever increasing problem of suitable disposal of contaminated or spent petroleum-based fluids. Water-content hydraulic fluids containing up to 95 percent or more water offer an obvious cost advantage over petroleum-based hydraulic fluids but suffer the disadvantage of having poor lubricating characteristics, thereby markedly reducing the service life of hydraulic pumps ordinarily used in industrial equipment. Although primarily used for transmitting forces, water-content hydraulic fluids necessarily must provide lubrication for impellers, support bearings, rings, gears, pistons, and other mechanical parts, in order to prevent excessive wear and fatigue failure of such parts.
It is known from U.S. Pat. No. 4,215,002 to prepare water-content hydraulic fluids by adding to water 0.5 to 4 wt.% of a blend of C.sub.6-18 alkylphosphonate or an amine adduct thereof and an ethoxylate of an acid or an alcohol containing from 3 to 20 ethoxy groups wherein the acid or alcohol is derived from fatty or synthetic sources.
U.S. Pat. No. 4,225,447 discloses an emulsifiable concentrate for use in water-in-oil fire-resistant hydraulic fluids comprising a lubricant and an alkenylsuccinic anhydride or a salt thereof.
U.S. Pat. No. 4,253,975 discloses an aqueous hydraulic fluid containing a metal dithiophosphate and a system of solubilizers therefor.
It is also known from U.S. Pat. No. 4,289,636 to provide aqueous lubricating compositions comprising water and a minor amount of a water-soluble amide derived from primary and secondary alkyl amines and succinic, tetrahydrophthalic or tetrahydrofuran tetracarboxylic acids. The amide is effective as a corrosion or antirust inhibitor. Aqueous lubricant formulations containing the amide in combination with other known special purpose additives provide a blend having good hard water stability characteristics.